Ever since the beginning of the series, Mercutio was a loyal and ambitious noble working under Lord Montague, which paid off when he was named Montague's heir. However, after Montague killed off his father, Mercutio became increasingly more unstable, until finally he lost his sanity and dealt the killing blow to Lord Montague.

Mercutio and Romeo met during the first episode of the series, although they had previous knowledge of each other before the beginning of the series. Throughout the events to follow, Mercutio constantly judged and berated Romeo for his optimism and positive outlook.